Steel factor controls the proliferation and differentiation of neonatal mouse epidermal melanocytes in culture

Mouse epidermal melanoblasts and melanocytes preferentially proliferated from disaggregated epidermal cell suspensions derived from newborn mouse skin in a serum-free melanocyte-proliferation medium (MDMD) and melanoblast-proliferation medium (MDMDF) supplemented with dibutyryl adenosine 3':5'-cyclic monophosphate (DBcAMP) and/or basic fibroblast growth factor (bFGF). Pure cultured primary melanoblasts and melanocytes were then further cultured with MDMD/MDMDF supplemented with steel factor (SLF) (keratinocyte depletion). SLF increased the number of melanoblasts and melanocytes as well as the proportion of differentiated melanocytes in the absence of keratinocytes. Flow cytometric analysis showed that melanoblasts and melanocytes in the S and G2/M phases of the cell cycle were increased by treatment with SLF. Moreover, an anti-SLF antibody added to MDMD/MDMDF from the initiation of the primary culture (in the presence of keratinocytes) inhibited the proliferation of melanoblasts and melanocytes as well as the differentiation of melanocytes. These results suggest that SLF is one of the keratinocyte-derived factors involved in regulating the proliferation and differentiation of neonatal mouse epidermal melanocytes in culture in cooperation with cAMP elevator and bFGF.     

Genetic and Epigenetic Control of the Proliferation and Differentiation of Mouse Epidermal Melanocytes in Culture

Serum-free culture of epidermal cell suspensions from neonatal skin of mice of strain C57BL/10JHir (B10) showed that α-melanocyte-stimulating hormone (α-MSH) was involved in regulating the differentiation of melanocytes by inducing tyrosinase activity, melanosome formation, and dendritogenesis. Dibutyryl adenosine 3′:5′-cyclic monophosphate (DB-cAMP) similarly induced the differentiation of melanocytes. On the other hand, DBcAMP induced the proliferation of epidermal melanocytes in culture in the presence of keratinocytes. Basic fibroblast growth factor (bFGF) was also shown to stimulate the sustained proliferation of undifferentiated melanoblasts in the presence of DBcAMP and keratinocytes. These results suggest that the proliferation and differentiation of mouse epidermal melanoblasts and melanocytes in culture are regulated by the three factors; namely, cAMP, bFGF, and keratinocyte-derived factors. Moreover, serum-free primary culture of mouse epidermal melanocytes derived from B10 congenic mice, which carry various coat color genes, showed that the coat color genes were involved in regulating the proliferation and differentiation of mouse epidermal melanocytes by controlling the proliferative rate, melanosome formation and maturation, and melanosome distribution.     

Granulocyte-macrophage colony-stimulating factor is a keratinocyte-derived factor involved in regulating the proliferation and differentiation of neonatal mouse epidermal melanocytes in culture

Mouse epidermal melanoblasts and melanocytes preferentially proliferated from disaggregated epidermal cell suspensions derived from newborn mouse skin in a serum-free melanocyte-proliferation medium (MDMD) and a melanoblast-proliferation medium (MDMDF) supplemented with dibutyryl adenosine 3':5'-cyclic monophosphate (DBcAMP) and/or basic fibroblast growth factor (bFGF). Pure cultured primary melanoblasts and melanocytes were further cultured with MDMD/MDMDF supplemented with granulocyte-macrophage colony-stimulating factor (GMCSF) from 14 days (keratinocyte depletion). GMCSF stimulated the number of melanoblasts/melanocytes as well as the percentage of differentiated melanocytes in keratinocyte-depleted cultures. Flow cytometry analysis showed that melanoblasts and melanocytes in the S and G(2)/M phases of the cell cycle were increased by the treatment with GMCSF. Moreover, anti-GMCSF antibody added to MDMD/MDMDF from the initiation of the primary culture (in the presence of keratinocytes) inhibited the proliferation of melanoblasts/melanocytes as well as the differentiation of melanocytes. Enzyme-linked immunosorbent assay of culture media revealed that GMCSF was secreted from keratinocytes, but not from melanocytes. These results suggest that GMCSF is one of the keratinocyte-derived factors involved in regulating the proliferation and differentiation of neonatal mouse epidermal melanoblasts/melanocytes in culture in cooperation with cAMP elevator and bFGF.     

Role of leukemia inhibitory factor in the regulation of the proliferation and differentiation of neonatal mouse epidermal melanocytes in culture

Mouse epidermal melanoblasts/melanocytes preferentially proliferated from disaggregated epidermal cell suspensions derived from newborn mouse skin in a serum-free melanoblast/melanocyte-proliferation medium supplemented with dibutyryl adenosine 3':5'-cyclic monophosphate (DBcAMP) and/or basic fibroblast growth factor (bFGF). Leukemia inhibitory factor (LIF) supplemented to the medium from initiation of primary culture increased the proliferation of melanoblasts or melanocytes as well as the differentiation of melanocytes. Pure cultured primary melanoblasts or melanocytes were further cultured with the medium supplemented with LIF from 14 days (keratinocyte depletion). LIF stimulated the proliferation of melanoblasts or melanocytes as well as the differentiation of melanocytes in the absence of keratinocytes. Moreover, anti-LIF antibody supplemented to the medium from initiation of primary culture inhibited the proliferation of melanoblasts or melanocytes as well as the differentiation of melanocytes. These results suggest that LIF is one of the keratinocyte-derived factors involved in regulating the proliferation and differentiation of neonatal mouse epidermal melanocytes in culture in cooperation with cAMP elevator and bFGF.     

Genetic and epigenetic control of the proliferation and differentiation of mouse epidermal melanocytes in culture.

Serum-free culture of epidermal cell suspensions from neonatal skin of mice of strain C57BL/10JHir (B10) showed that alpha-melanocyte-stimulating hormone (alpha-MSH) was involved in regulating the differentiation of melanocytes by inducing tyrosinase activity, melanosome formation, and dendritogenesis. Dibutyryl adenosine 3':5'-cyclic monophosphate (DBcAMP) similarly induced the differentiation of melanocytes. On the other hand, DBcAMP induced the proliferation of epidermal melanocytes in culture in the presence of keratinocytes. Basic fibroblast growth factor (bFGF) was also shown to stimulate the sustained proliferation of undifferentiated melanoblasts in the presence of DBcAMP and keratinocytes. These results suggest that the proliferation and differentiation of mouse epidermal melanoblasts and melanocytes in culture are regulated by the three factors; namely, cAMP, bFGF, and keratinocyte-derived factors. Moreover, serum-free primary culture of mouse epidermal melanocytes derived from B10 congenic mice, which carry various coat color genes, showed that the coat color genes were involved in regulating the proliferation and differentiation of mouse epidermal melanocytes by controlling the proliferative rate, melanosome formation and maturation, and melanosome distribution.     

Hepatocyte growth factor controls the proliferation of cultured epidermal melanoblasts and melanocytes from newborn mice

Mouse epidermal melanoblasts and melanocytes preferentially proliferated from disaggregated epidermal cell suspensions derived from newborn mouse skin in a serum-free melanocyte-proliferation medium (MDMD) and melanoblast-proliferation medium (MDMDF) supplemented with dibutyryl adenosine 3':5'-cyclic monophosphate (DBcAMP) and/or basic fibroblast growth factor (bFGF). Pure cultured primary melanoblasts and melanocytes were further cultured with MDMD/MDMDF supplemented with hepatocyte growth factor (HGF) from 14 days (keratinocyte depletion). The HGF increased the number of melanoblasts and melanocytes, but not the percentage of differentiated melanocytes in the melanoblast-melanocyte population in the absence of keratinocytes. Flow cytometry analysis showed that melanoblasts and melanocytes in the S and/or G2/M phases of the cell cycle were increased by the treatment with HGF. Moreover, an anti-HGF antibody supplemented to MDMD/MDMDF from the initiation of the primary culture (in the presence of keratinocytes) inhibited the proliferation of melanoblasts and melanocytes, but not the differentiation of melanocytes. These results suggest that HGF is a keratinocyte-derived factor involved in regulating the proliferation of epidermal melanoblasts and melanocytes from newborn mice in cooperation with cAMP elevators and/or bFGF.     

Granulocyte-macrophage colony-stimulating factor (GM-CSF) controls the proliferation and differentiation of mouse epidermal melanocytes from pigmented spots induced by ultraviolet radiation B

Repeated exposure of ultraviolet radiation B (UVB) on the dorsal skin of hairless mice induces the development of pigmented spots long after its cessation. The proliferation and differentiation of epidermal melanocytes in UVB-induced pigmented spots are greatly increased, and those effects are regulated by keratinocytes rather than by melanocytes. However, it remains to be resolved what factor(s) derived from keratinocytes are involved in regulating the proliferation and differentiation of epidermal melanocytes. In this study, primary melanoblasts (c. 80%) and melanocytes (c. 20%) derived from epidermal cell suspensions of mouse skin were cultured in a basic fibroblast growth factor-free medium supplemented with granulocyte-macrophage colony-stimulating factor (GM-CSF). GM-CSF induced the proliferation and differentiation of melanocytes in those keratinocyte-depleted cultures. Moreover, an antibody to GM-CSF inhibited the proliferation of melanoblasts and melanocytes from epidermal cell suspensions derived from the pigmented spots of UV-irradiated mice, but not from control mice. Further, the GM-CSF antibody inhibited the proliferation and differentiation of melanocytes co-cultured with keratinocytes derived from UV-irradiated mice, but not from control mice. The quantity of GM-CSF secreted from keratinocytes derived from the pigmented spots of UV-irradiated mice was much greater than that secreted from keratinocytes derived from control mice. Moreover, immunohistochemistry revealed the expression of GM-CSF in keratinocytes derived from the pigmented spots of skin in UV-irradiated mice, but not from normal skin in control mice. These results suggest that GM-CSF is one of the keratinocyte-derived factors involved in regulating the proliferation and differentiation of mouse epidermal melanocytes from UVB-induced pigmented spots.     

Granulocyte‐Macrophage Colony‐Stimulating Factor (GM‐CSF) Controls the Proliferation and Differentiation of Mouse Epidermal Melanocytes from Pigmented Spots Induced by Ultraviolet Radiation B

Repeated exposure of ultraviolet radiation B (UVB) on the dorsal skin of hairless mice induces the development of pigmented spots long after its cessation. The proliferation and differentiation of epidermal melanocytes in UVB‐induced pigmented spots are greatly increased, and those effects are regulated by keratinocytes rather than by melanocytes. However, it remains to be resolved what factor(s) derived from keratinocytes are involved in regulating the proliferation and differentiation of epidermal melanocytes. In this study, primary melanoblasts (c. 80%) and melanocytes (c. 20%) derived from epidermal cell suspensions of mouse skin were cultured in a basic fibroblast growth factor‐free medium supplemented with granulocyte‐macrophage colony‐stimulating factor (GM‐CSF). GM‐CSF induced the proliferation and differentiation of melanocytes in those keratinocyte‐depleted cultures. Moreover, an antibody to GM‐CSF inhibited the proliferation of melanoblasts and melanocytes from epidermal cell suspensions derived from the pigmented spots of UV‐irradiated mice, but not from control mice. Further, the GM‐CSF antibody inhibited the proliferation and differentiation of melanocytes co‐cultured with keratinocytes derived from UV‐irradiated mice, but not from control mice. The quantity of GM‐CSF secreted from keratinocytes derived from the pigmented spots of UV‐irradiated mice was much greater than that secreted from keratinocytes derived from control mice. Moreover, immunohistochemistry revealed the expression of GM‐CSF in keratinocytes derived from the pigmented spots of skin in UV‐irradiated mice, but not from normal skin in control mice. These results suggest that GM‐CSF is one of the keratinocyte‐derived factors involved in regulating the proliferation and differentiation of mouse epidermal melanocytes from UVB‐induced pigmented spots.     

Melanocyte stimulating hormone induces the differentiation of mouse epidermal melanocytes in serum-free culture.

In serum-free primary culture of dissociated mouse epidermal cells, alpha-melanocyte stimulating hormone (alpha-MSH) and dibutyryl cyclic AMP (DBcAMP) induced the differentiation of melanocytes. Moreover, the proliferation of melanocytes was also induced in the dishes cultured with DBcAMP, but not with alpha-MSH. In order to clarify the role of keratinocytes in melanocyte proliferation and differentiation, pure cultures of keratinocytes were established in serum-free medium. Subconfluent primary keratinocytes were trypsinized and seeded into pure primary melanoblasts cultured with serum-free medium that did not contain alpha-MSH or DBcAMP. Melanoblasts were cultured with alpha-MSH or DBcAMP in the presence or absence of keratinocytes. alpha-MSH failed to induce melanocyte differentiation in the absence of keratinocytes. DBcAMP failed to induce melanocyte proliferation in the absence of keratinocytes, although it induced melanocyte differentiation even in the absence of keratinocytes. These results suggest that keratinocyte-derived factors are required not only for the induction of melanocyte differentiation by alpha-MSH but also for the induction of melanocyte proliferation by DBcAMP.     

Keratinocytes control the proliferation and differentiation of cultured epidermal melanocytes from ultraviolet radiation B-induced pigmented spots in the dorsal skin of hairless mice

Long-term exposure of ultraviolet radiation B (UVB)-induced pigmented spots in the dorsal skin of hairless mice of Hos:(HR-1 X HR//De) F1. Previous study showed that the proliferative and differentiative activities of cultured epidermal melanoblasts/melanocytes from UVB-induced pigmented spots increased with the development of the pigmented spots. To determine whether the increase in the proliferative and differentiative activities of epidermal melanoblasts/melanocytes was brought about by direct changes in melanocytes, or by indirect changes in surrounding keratinocytes, pure cultured melanoblasts/melanocytes and keratinocytes were prepared and co-cultured in combination with control and irradiated mice in a serum-free culture medium. Keratinocytes from irradiated mice stimulated the proliferation and differentiation of both neonatal and adult non-irradiated melanoblasts/melanocytes more greatly than those from non-irradiated mice. In contrast, both non-irradiated and irradiated adult melanocytes proliferated and differentiated similarly when they were co-cultured with irradiated adult keratinocytes. These results suggest that the increased proliferative and differentiative activities of mouse epidermal melanocytes from UVB-induced pigmented spots are regulated by keratinocytes, rather than melanocytes.     

Keratinocytes Control the Proliferation and Differentiation of Cultured Epidermal Melanocytes from Ultraviolet Radiation B‐Induced Pigmented Spots in the Dorsal Skin of Hairless Mice

Long‐term exposure of ultraviolet radiation B (UVB)‐induced pigmented spots in the dorsal skin of hairless mice of Hos:(HR‐1 X HR//De) F₁. Previous study showed that the proliferative and differentiative activities of cultured epidermal melanoblasts//melanocytes from UVB‐induced pigmented spots increased with the development of the pigmented spots. To determine whether the increase in the proliferative and differentiative activities of epidermal melanoblasts//melanocytes was brought about by direct changes in melanocytes, or by indirect changes in surrounding keratinocytes, pure cultured melanoblasts//melanocytes and keratinocytes were prepared and co‐cultured in combination with control and irradiated mice in a serum‐free culture medium. Keratinocytes from irradiated mice stimulated the proliferation and differentiation of both neonatal and adult non‐irradiated melanoblasts//melanocytes more greatly than those from non‐irradiated mice. In contrast, both non‐irradiated and irradiated adultmelanocytes proliferated and differentiated similarly when they were co‐cultured with irradiated adult keratinocytes. These results suggest that the increased proliferative and differentiative activities of mouse epidermal melanocytes from UVB‐induced pigmented spots are regulated by keratinocytes, rather than melanocytes.     

Changes in the proliferation and differentiation of neonatal mouse pink-eyed dilution melanocytes in the presence of excess tyrosine

Changes in the proliferation and differentiation of epidermal melanocytes derived from newborn mice wild-type at the pink-eyed dilution (p) locus (P/P) and from congenic mice mutant at that locus (p/p) were investigated in serum-free primary culture, with or without the addition of L-Tyr. Incubation with added L-Tyr inhibited the proliferation of P/P melanocytes in a concentration-dependent manner and inhibition was gradually augmented as the donor mice aged. In contrast, L-Tyr stimulated the proliferation of p/p melanoblasts-melanocytes derived from 0.5-day-old mice, but inhibited their proliferation when derived from 3.5- or 7.5-day-old mice. L-Tyr stimulated the differentiation of P/P melanocytes. However, almost all cells were undifferentiated melanoblasts in control cultures derived from 0.5-, 3.5- and 7.5-day-old p/p mice, but L-Tyr induced their differentiation as the age of the donor mice advanced. The content of the eumelanin marker, pyrrole-2,3,5-tricarboxylic acid as well as the pheomelanin marker, 4-amino-3-hydroxyphenylalanine in p/p melanocytes was greatly reduced compared with P/P melanocytes. However, the contents of eumelanin and its precursor, 5,6-dihydroxyindole-2-carboxylic acid, as well as the contents of pheomelanin and its precursor, 5-S-cysteinyldopa in culture media from p/p melanocytes were similar to those of P/P melanocytes at all ages tested. L-Tyr increased the content of eumelanin and pheomelanin two- to threefold in cultured cells and media derived from 0.5-, 3.5- and 7.5-day-old mice. These results suggest that the proliferation of p/p melanoblasts-melanocytes is stimulated by L-Tyr, and that the differentiation of melanocytes is induced by L-Tyr as the age of the donor mice advanced, although eumelanin and pheomelanin fail to accumulate in p/p melanocytes and are released from them at all ages of skin development.     

Role of keratinocyte-derived factors involved in regulating the proliferation and differentiation of mammalian epidermal melanocytes

Melanocytes characterized by the activities of tyrosinase, tyrosinase-related protein (TRP)-1 and TRP-2 as well as by melanosomes and dendrites are located mainly in the epidermis, dermis and hair bulb of the mammalian skin. Melanocytes differentiate from melanoblasts, undifferentiated precursors, derived from embryonic neural crest cells. Because hair bulb melanocytes are derived from epidermal melanoblasts and melanocytes, the mechanism of the regulation of the proliferation and differentiation of epidermal melanocytes should be clarified. The regulation by the tissue environment, especially by keratinocytes is indispensable in addition to the regulation by genetic factors in melanocytes. Recent advances in the techniques of tissue culture and biochemistry have enabled us to clarify factors derived from keratinocytes. Alpha-melanocyte-stimulating hormone, adrenocorticotrophic hormone, basic fibroblast growth factor, nerve growth factor, endothelins, granulocyte-macrophage colony-stimulating factor, steel factor, leukemia inhibitory factor and hepatocyte growth factor have been suggested to be the keratinocyte-derived factors and to regulate the proliferation and/or differentiation of mammalian epidermal melanocytes. Numerous factors may be produced in and released from keratinocytes and be involved in regulating the proliferation and differentiation of mammalian epidermal melanocytes through receptor-mediated signaling pathways.     

Basic fibroblast growth factor stimulates the sustained proliferation of mouse epidermal melanoblasts in a serum-free medium in the presence of dibutyryl cyclic AMP and keratinocytes.

Basic fibroblast growth factor (bFGF) stimulated the sustained proliferation of mouse epidermal melanoblasts derived from epidermal cell suspensions in a serum-free medium supplemented with dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP). The melanoblasts could be subcultured in the serum-free medium supplemented with the two factors in the presence of keratinocytes, but not in the absence of keratinocytes. In these conditions, some melanoblasts proliferated without differentiating for more than 20 days including a subculture. This is the first report of a successful culture of melanoblasts from mammalian skin. This culture system is expected to clarify further markers for melanoblasts and requirements for their proliferation and differentiation.     

Role of keratinocyte‐derived factors involved in regulating the proliferation and differentiation of mammalian epidermal melanocytes

Melanocytes characterized by the activities of tyrosinase, tyrosinase‐related protein (TRP)‐1 and TRP‐2 as well as by melanosomes and dendrites are located mainly in the epidermis, dermis and hair bulb of the mammalian skin. Melanocytes differentiate from melanoblasts, undifferentiated precursors, derived from embryonic neural crest cells. Because hair bulb melanocytes are derived from epidermal melanoblasts and melanocytes, the mechanism of the regulation of the proliferation and differentiation of epidermal melanocytes should be clarified. The regulation by the tissue environment, especially by keratinocytes is indispensable in addition to the regulation by genetic factors in melanocytes. Recent advances in the techniques of tissue culture and biochemistry have enabled us to clarify factors derived from keratinocytes. Alpha‐melanocyte‐stimulating hormone, adrenocorticotrophic hormone, basic fibroblast growth factor, nerve growth factor, endothelins, granulocyte‐macrophage colony‐stimulating factor, steel factor, leukemia inhibitory factor and hepatocyte growth factor have been suggested to be the keratinocyte‐derived factors and to regulate the proliferation and/or differentiation of mammalian epidermal melanocytes. Numerous factors may be produced in and released from keratinocytes and be involved in regulating the proliferation and differentiation of mammalian epidermal melanocytes through receptor‐mediated signaling pathways.     

Effects of genic substitution at the pink-eyed dilution locus on the proliferation and differentiation of mouse epidermal melanocytes in vivo and in vitro

Cells positive to the dopa reaction (melanocytes) as well as to the combined dopa-premelanin reaction (melanoblasts and melanocytes) in the epidermis of C57BL/10JHir-p/p (pink-eyed dilution) mice were fewer and less reactive than in C57BL/10JHir (black, P/P) mice, suggesting that the proliferation and differentiation of p/p melanocytes are inhibited. To confirm the inhibitory effects of p gene on the proliferation and differentiation of epidermal melanocytes, we cultured epidermal cell suspensions of neonatal skins from P/P and p/p in a serum-free medium. The proliferation and differentiation of p/p melanoblasts/melanocytes in primary culture were greatly inhibited as compared to P/P melanoblasts/melanocytes. The morphology of p/p melanoblasts/melanocytes cultured in melanocyte growth medium, though non-pigmented, was similar to P/P melanocytes; namely, dendritic, polygonal, or epithelioid. About 8% of p/p cells cultured in melanocyte growth medium were positive to the dopa reaction, and about 25% were reactive to the combined dopa-premelanin reaction. Eumelanin content in p/p was extremely reduced compared to P/P. The immunocytochemical staining of p/p melanoblasts/melanocytes revealed that they are negative to tyrosinase, but reactive to tyrosinase-related protein (TRP)-1, TRP-2, and c-kit. However, the reactivities in p/p were lower than in P/P. Although the differentiation of p/p melanoblasts was not induced by endothelin (ET)-1, ET-2, and ET-3, the proliferation of p/p melanoblasts was stimulated by them. These results suggest for the first time that p gene exerts its influence on the proliferative activities of mouse epidermal melanoblasts by affecting the regulatory mechanisms dependent on the function of ETs.